Engine breathing and oil consumption.

Technical MGB discussion
Dave Wheatley
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Location: SW Scotland

Engine breathing and oil consumption.

Post by Dave Wheatley » Tue Apr 16, 2019 10:29 am

Car is a standard 1978 GT.

I put the car back on the road on 1st April after a winter lay up. During the lay up I returned the engine breathing back to standard from the system that a preious owner had put in - open pipe from the side plate with a cloth filter, and the breather pipes on the hifs joined together. Oil filler cap is the vented type and is clear.

I used the car regularly last October doing a few hundred miles. Oil consumption was slight.

Now with the standard system installed, the oil consumption is horrendous, with a cloud of smoke following the car when warmed up.

Compression is good 170 - 175 on all 4 cylinders.

Any ideas what could be wrong? Blocked breather pipes at the carbs? Breather pipe from the side plate is well clear.

I'm returning to the old owner's system today to see if that makes a difference.

I'm stumped!
1978 MGB GT
1931 Austin 7 RM
1955 Standard 10
1972 Ford Cortina
No modern!

Vic Butler
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Location: North West Hampshire

Re: Engine breathing and oil consumption.

Post by Vic Butler » Tue Apr 16, 2019 10:42 am

That sounds like the reason why the previous owner altered the breather.
It appears that the engine is burning its oil through the closed breather? Are there any fumes with the oil filler cap removed?
It could be a blockage somewhere. Best to check all the breather pipes and remove the tappet cover and clean out the gauze.
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine

Dave Wheatley
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Joined: Fri Sep 28, 2018 4:55 pm
Forename: Dave
Surname: Wheatley
Location: SW Scotland

Re: Engine breathing and oil consumption.

Post by Dave Wheatley » Tue Apr 16, 2019 12:29 pm

Thanks Vic.

I've just done a 15 mile run after connecting the carbs breather tubes together, and run a pipe from the side plate pipe to a catch tank.

Result no smoke even after 10 minutes ticking over. Nothing in the catch tank. Very little breathings from either the filler cap or the side plate tube

As far as I can check, the pipe work on the standard breather system was all clear.

So what was going on. One point is that I checked the plugs before I reverted to the previous owner's system, and plugs 1 and 2 were very oily, 3 and 4 were fine. Just checked after the run, and 1 and 2 now fine.

I'm suspecting that 1 and 2 cylinder carb is needing attention - blocked breather tube?.
1978 MGB GT
1931 Austin 7 RM
1955 Standard 10
1972 Ford Cortina
No modern!

Vic Butler
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Joined: Wed Dec 21, 2016 6:07 pm
Forename: Vic
Surname: Butler
Location: North West Hampshire

Re: Engine breathing and oil consumption.

Post by Vic Butler » Tue Apr 16, 2019 2:06 pm

David, the standard breather pipe set up on rubber bumper B's is a short pipe from the side plate to a Y piece, a short pipe to the front carburettor and a longer pipe from the other arm of the Y piece to the rear carburettor. Although my BGT has HS6's I retained this system for the breather. Is this the breather set up on yours.
If plugs 1&2 only are oily then it points to a problem with the breather on the front carburettor when using the original system.
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine

Dave Wheatley
Posts: 122
Joined: Fri Sep 28, 2018 4:55 pm
Forename: Dave
Surname: Wheatley
Location: SW Scotland

Re: Engine breathing and oil consumption.

Post by Dave Wheatley » Tue Apr 16, 2019 2:45 pm

Thanks again Vic. My standard breather setup which I have replaced with with an extension to a catch tank from the side plate pipe and joined the 2 stubs on the carbs was as you describe, except I used my own pipework and y piece.

I've had a check round the front carb as far as I can without taking it off, and all seems well. Breather tube is clear.

I think I will just run it a while with the modified setup, and monitor the plugs and catch tank.
1978 MGB GT
1931 Austin 7 RM
1955 Standard 10
1972 Ford Cortina
No modern!

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Charles Farran
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Forename: Charles
Surname: Farran
Location: Warwickshire

Re: Engine breathing and oil consumption.

Post by Charles Farran » Tue Apr 16, 2019 4:42 pm

David,
My standard breather set up (with HIF Carbs) was as Vic says in his post of 2.06 pm (with the rocker cover cap being the standard plastic type with built in filter). I had to remove the tappet chest covers 18 months ago to cure oil leaks. I took the opportunity to clean out the gauze in the front cover which are known to clog up over time / in frequent oil changes. I also cleaned out the breather pipes as well. Access to the covers (particularly the rear one) was for me impossible without removing the exhaust manifold. (If you do remove the covers i would recommend you use an MGA cork gasket for the front cover & a rubber MGB one for the rear & also be sure to use a new rubber gasket in the cup washers that the holding screws utilise as they will leak if not renewed).
Cheers,Charles
1980 Roadster

Dave Wheatley
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Location: SW Scotland

Re: Engine breathing and oil consumption.

Post by Dave Wheatley » Tue Apr 16, 2019 6:53 pm

Ta Charles, Tappet chest breather pipe is clear I think. I can blow down it with no resistance. In view of your comments re removal of tappet chest covers, I'm going to leave well alone for now. Probably going to do an unleaded conversion later this year, so I can investigate the covers then.

Still a mystery though why the oil consumption should be so high. My Standard 10 breathes heavily and has a similar setup to my modified one, but still manages around 300 mpg on oil.
1978 MGB GT
1931 Austin 7 RM
1955 Standard 10
1972 Ford Cortina
No modern!

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Charles Farran
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Joined: Fri Oct 31, 2014 11:08 am
Forename: Charles
Surname: Farran
Location: Warwickshire

Re: Engine breathing and oil consumption.

Post by Charles Farran » Tue Apr 16, 2019 8:35 pm

Dave,
I assume you haven't put synthetic oil in on your last oil change as this can create the symptoms you have following years of normal mineral 20 / 50 (per Roger Williams expert guide to MGB & MGBGT PROBLEMS & HOW TO SOLVE THEM)?
Cheers, Charles
1980 Roadster

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Charles Farran
Posts: 210
Joined: Fri Oct 31, 2014 11:08 am
Forename: Charles
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Location: Warwickshire

Re: Engine breathing and oil consumption.

Post by Charles Farran » Tue Apr 16, 2019 8:42 pm

Dave,
I assume your coolant problem was resolved & that it didn't have a knock on effect to the oil loss even though you seem to have checked compression?
Cheers, Charles
1980 Roadster

Dave Wheatley
Posts: 122
Joined: Fri Sep 28, 2018 4:55 pm
Forename: Dave
Surname: Wheatley
Location: SW Scotland

Re: Engine breathing and oil consumption.

Post by Dave Wheatley » Wed Apr 17, 2019 10:54 am

My Standard 10 of course does 300 mpp, and not 300 mpg!

Charles, I changed the oil and filter just before recommissioning in April, and used 20/50 mineral. Cooling appears to be back to normal now. I'll be doing a 50 mile run today, so that should tell me whether or not, cooling, oil consumption and my (so far unreported on here)misfire are fixed.

Just a little tale about the misfire. When I got the car last September, I reported that a previous owner had put too long a scroo holding the points on. This had the effect of disabling the vacuum advance by locking the moving and fixed plates in the distributor together. So during the winter lay up I replaced the scroo, and the vacuum advance was OK.
Roll on to April this year, and apart from the cooling and oil consumption problems, I now had a frequent misfire. Anyway after checking everything - plugs, points, coil etc., I offered up a spare condensor, connecting up direct to the coil, and bingo no misfire. Dud condensor then? On inspection of the distributor and much head scratching, I eventually realised that the pigtail wire that earths the moving plate to the fixed plate was not present and thus causing an intermittent misfire. Bingo for the misfire - another previous owner modification which worked instead of fixing the original problem.

Anyway, a new pigtail is on its way, but meanwhile I continue to run with the condensor attached at the coil as well as the original one in the distributor. I suppose it could be a dud condensor though..................
1978 MGB GT
1931 Austin 7 RM
1955 Standard 10
1972 Ford Cortina
No modern!

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